Photochromic material includes molecules or molecule aggregates which can reversibly take the forms of two isomers having different states by photoisomerization. The photochromic material can be utilized as photonics materials such as optical memory media and optical display materials, because the photochromic material can change not only its color but also its various other physical properties—such as refractive index, dielectric constant, and oxidation/reduction potential under irradiation of light.
Japanese Unexamined Patent Publication No. H3-261782 discloses a photochromic material belonging to the diheteroarylethane class, having methoxy groups at two reactive positions participating in ring closing/ring opening reactions, as expressed by the following formula:

The record or image of the optical memory medium or optical display material of the photochromic material may disappear under ambient light such as a room light. When the quantum yield of ring opening reaction (hereinafter, referred to as “ring opening quantum yield”) of a compound, belonging to the diarylethene class, in the closed-ring form is in the order of 10−2, the record or image will disappear almost completely in several hours under fluorescent room light.
The aforementioned compound belonging to the diheteroarylethene class disclosed in Japanese Unexamined Patent Publication No. H3-261782 has a ring opening quantum yield of 3.3×10−2, which is larger than 10−2.